Snails are an intermediate host used by the parasite during part of its life cycle.
"One of the great challenges in studying the diversity-disease link has been collecting data from enough replicate systems to differentiate the influence of diversity from background 'noise,'" Johnson said.
"By collecting data from hundreds of ponds and thousands of amphibian hosts, we were able to provide a rigorous test of this hypothesis, which has relevance to a wide range of disease systems."
The researchers buttressed field observations with laboratory tests designed to measure how prone to infection each amphibian species is, and by creating pond replicas using large plastic tubs stocked with tadpoles that were exposed to a known number of parasites.
All the experiments told the same story.
Greater biodiversity reduced the number of amphibian infections and the number of deformed frogs.
The scientists spent three years sampling 345 wetlands and recording malformations--which include missing, misshapen or extra sets of hind legs--caused by parasitic infections in 24,215 amphibians.
The results showed that ponds with half a dozen amphibian species had a 78 percent reduction in parasite transmission compared to ponds with just one amphibian species.
The reason for the decline in parasitic infections as biodiversity increases is likely related to the fact that ponds add amphibian species in a predictable pattern, with the first species to appear being the most prone to infection and the later species to appear being the least prone.
The researchers found that in a pond with just one type of amphibian, that amphibian was almost always the Pacific chorus frog, a creature that's able to rapidly reproduce and quickly colonize wetland habitats, but which is also especially vulnerable to infection and parasite-induced
|Contact: Cheryl Dybas|
National Science Foundation